A check valve is generally a valve that allows fluid (i.e., liquid or gas) to flow through it in only one direction. Common designs for check valves can include a movable portion, such as a disk or a ball, which is sized to block an inlet of the valve. When sufficient pressure is applied to the inlet, sometimes referred to as the cracking pressure, the movable portion can be unseated so that fluid can flow past the movable portion and through the valve. If higher pressure is developed in the opposite direction or fluid flow stops (e.g., the pump stops), the movable portion is pressed back against the inlet to prevent any fluid from flowing upstream of the valve.
Although valves based on this simple design have been used for decades, such valves often exhibit problems in one or more of pressure drop, noise, erosion, corrosion, vibration, and cavitation. It is believed that many of these problems arise as a result of turbulent flow entering the valve inlet, which can cause uneven wearing of the valve inlet and the movable portion. Further, the turbulent flow against the movable portion can cause the movable portion to rotate in place, resulting in energy losses of the fluid flowing through the valve.
Reduction in the turbulent flow through the valve can be accomplished by ensuring that the fluid flows uniformly to the valve inlet. One way of ensuring this uniform flow is to provide a minimum length of straight pipe that the fluid must flow through before reaching the valve. For instance, it is often recommended that a check valve be installed no less than 5 pipe diameters downstream from a reducer, expander, bend, or isolating valve, and no less than 2 diameters upstream of such a component. Although such system designs can improve valve operation, the amount of space required for a long run of straight pipe can be burdensome in many situations. As a result, improved designs for a check valve would be desirable to improve valve efficiency, operation, and longevity without requiring large-scale piping system constraints.